drop table course; create table course ( id integer, teacherNo integer, teacherDesc varchar2(100), teacherName varchar2(50), courseName varchar2(50) ); insert into course values(1,100,'Mr.zhang','ZhangSan','English'); insert into course values(2,101,'Mr.wang','WangWu','History'); insert into course values(2,101,'Mr.wang','WangWu','Chinese'); update course set teacherDesc='Good Teacher' where teacherNo=101; commit; drop table teacher; create table teacher( id integer, teacherDesc varchar2(100), teacherName varchar2(50) ); insert into teacher values(100,'Mr.zhang','ZhangSan'); insert into teacher values(101,'Mr.wang','WangWu'); update teacher set teacherDesc='Excellent Teacher' where id=101; commit; select c.teacherdesc, c.teachername, t.teacherdesc, t.teachername from course c, teacher t where c.teacherno = t.id and (c.teacherdesc != t.teacherdesc or c.teachername != t.teachername); update course c set (c.teacherdesc, c.teachername) = (select t.teacherdesc, t.teachername from teacher t where c.teacherno = t.id and (c.teacherdesc != t.teacherdesc or c.teachername != t.teachername)) where exists (select 1 from teacher t where c.teacherno = t.id and (c.teacherdesc != t.teacherdesc or c.teachername != t.teachername)); commit; select c.teacherdesc, c.teachername, t.teacherdesc, t.teachername from course c, teacher t where c.teacherno = t.id and (c.teacherdesc != t.teacherdesc or c.teachername != t.teachername); select c.teacherdesc, c.teachername, t.teacherdesc, t.teachername from course c, teacher t where c.teacherno = t.id;
update时报ORA-01779：
数据准备：
CREATE TABLE test1 ( id integer primary key, num integer ); INSERT INTO test1 VALUES (1,0); INSERT INTO test1 VALUES (2,0); INSERT INTO test1 VALUES (3,0); INSERT INTO test1 VALUES (4,0); CREATE TABLE test2 ( id integer, num integer, upd integer ); INSERT INTO test2 VALUES (1,10, 0); INSERT INTO test2 VALUES (2,20, 1); commit;
执行如下更新语句会报错：ORA-01779: 无法修改与非键值保存表对应的列
01779, 00000, "cannot modify a column which maps to a non key-preserved table"
// *Cause: An attempt was made to insert or update columns of a join view which
// map to a non-key-preserved table.
// *Action: Modify the underlying base tables directly.
UPDATE (SELECT T1.ID ID1, T1.NUM NUM1, T2.ID ID2, T2.NUM NUM2
FROM TEST1 T1, TEST2 T2
WHERE T1.ID = T2.ID
AND T2.UPD = 1)
SET NUM1 = NUM2;
这个错误的意思是，子查询的结果中，更新数据源(test2)的内容不唯一，导致被更新对象(test1)中的一行可能对应数据源(test2)中的多行。
本例中，test2表的id不唯一，因此test2表中可能存在id相同但是num不相同的数据，这种数据是无法用来更新 test1 的。【这个报错属于事前检查，没有通过校验】
解决方法就是保证数据源的唯一性，例如本例中可以为test2.id创建一个唯一索引：
CREATE UNIQUE INDEX test2_idx_001 ON test2 (id);
之后上面的更新就可以执行了。
也可以使用如下命令来使用test2中记录具有唯一性
alter table test2 modify id unique;
另外也可以强制 Oracle 执行，方法是加上 BYPASS_UJVC 注释。
UPDATE (SELECT /*+ BYPASS_UJVC */
T1.ID ID1, T1.NUM NUM1, T2.ID ID2, T2.NUM NUM2
FROM TEST1 T1, TEST2 T2
WHERE T1.ID = T2.ID
AND T2.UPD = 1)
SET NUM1 = NUM2;
BYPASS_UJVC的作用是跳过Oracle的键检查。
这样虽然能够执行了，但是如果test2中存在不唯一的数据，test1就会被更新多次而导致意想不到的结果。【有风险，不建议使用】
http://www.linuxidc.com/Linux/2012-08/69089.htm
